The subject matter disclosed herein relates generally to radio frequency (RF) coils, and more particularly to an inductor used in an RF coil.
Magnetic Resonance Imaging (MRI) systems include a magnet, such as a superconducting magnet that generates a temporally constant (i.e., uniform and static) primary or main magnetic field. MRI data acquisition is accomplished by exciting magnetic moments within the primary magnetic field using magnetic gradient coils. For example, in order to image a region of interest, the magnetic gradient coils are energized to impose a magnetic gradient to the primary magnetic field. Transmit radio-frequency (RF) coils are then pulsed to create RF magnetic field pulses in a bore of an MRI scanner to selectively excite a volume corresponding to the region of interest in order to acquire MR images of the region of interest using receive RF coils. During the transmission of the RF magnetic field pulses, the receive RF coils are decoupled or detuned. Decoupling of the receive coil array is achieved using decoupling circuits that include an inductor connected in parallel with a capacitor. The inductor and capacitor may also be combined in series or used alone in the phased array circuitry as a choke for RF currents in DC lines, in T/R switches, and/or Multiplexing Boards (MuxBoards). The magnetic field exhibited by these inductors must be confined within their physical dimensions so that no coupling occurs between the inductors and other components in the circuitry.
Conventional RF coils include usually include many inductors that are typically resonated with capacitors by creating parallel resonant tank circuits. In general, when the reactance of the capacitor is substantially equal to the reactance of the inductor the tank circuit is in resonance.
During operation, it is desirable to utilize an inductor having a relatively good magnetic field confinement. However, due to the structure of the conventional inductor, the conventional inductor may exhibit magnetic dipole radiation. For example, it is known that a closed loop is an excellent example of the magnetic dipole. Decomposed into multipoles, the closed loop has only a first term corresponding to the magnetic dipole, different from zero. By repeating the loop geometry along an axis, a spiral having an increased dipole moment and proportional to the number of turns is created. The conventional method of confining this type of inductor is to make the ends meet, thus creating a torus-shaped inductor. However, conventional torus-shaped inductors do not totally confine the magnetic field. Rather, in operation, the conventional torus-shaped inductor has a small, but important, magnetic dipole radiation component that is caused by a tilt in wrapping the single conductor around the torus surface. This tilt creates a certain magnetic dipole radiation that may affect the conventional torus-shaped inductor's coupling to neighboring components.